Can't be used for the instant transmission of data
Lies for children explanation as to why it doesn't give Instant communication:
Essentially you have two randomly shuffled packs of cards that you have NOT looked at. The change to the entangled particles essentially is the same as if both packs of card are re-ordered (and still match).
When you look to see the order the entanglement is lost.
Thus by being clever you can tell if quantum entangled communication has been tampered with (a man in the middle attack may be impossible), but actual transmission of actual information is limited by light speed.
So an "ansible" or other faster than light communications isn't stopped by practical limitations but by basic physics. Only entangled particles ever "know" there has been a change. The two observers can agree to look at the same time and compare results. Obviously the agreement to look and the measurement of state are both communications limited to light speed or slower.
Like all quantum mechanics, just when you feel you've grasped it, you realise it's not comprehensible.